The invention relates to data communication. More particularly, the invention relates to a method and system for adaptively removing interference from a received high speed data signal.
It is desirable in high speed data communication to increase the distance the high speed signal travels through transmission media from a transmitter to a receiver. Unfortunately, data signals carried by lossy media such as twisted-pair copper wire, or even fiber optic cable, are subject to amplitude and phase distortions that are frequency and cable length dependent. Moreover, media losses may occur on printed wiring boards due to “skin effect.” Uncompensated, such media losses result in both amplitude and timing jitter, such as intersymbol interference (ISI), which imposes practical limitations on the attainable bit error rate (BER) performance, and consequently the link budget. Amplitude and phase equalization is typically employed to correct the distortions at the receiver.
Adaptive receiver equalization systems have been employed to correct distortions or interference in high speed data communications networks such as ATM (155 MBits/s), 100BaseTX Ethernet (100 MBits/s) and FDDI TP-PMD (Twisted-Pair FDDI, 100 Mbits/s).
The prior art systems typically include some kind of variable attenuation, either through amplifiers and/or filters having variable gain, or through a variable attenuator being placed in the path of the signal. These systems have disadvantages from a power usage perspective, since a portion of the received signal is dissipated. Moreover, the prior art systems often require a fixed amplitude reference to control equalization.
For example, U.S. Pat. No. 5,987,065 describes an adaptive equalizer using two high pass filters having variable gain, the output of each connected to one of two respective peak detectors. The outputs of the two peak detectors are compared in a differential amplifier, the output of which is used to control the variable gain of one of the filters. The other filter's gain is held constant to act as a fixed reference for comparison.
Transversal filters, such as the one described in U.S. Pat. No. 5,920,594, have also been described for use in waveform equalization in the prior art. These designs, however, are difficult to implement in practice due to the tight tolerances required for the tap element, the precision required in the digital-to-analog converter, and other factors.